1. Field of the Invention
The present invention relates to a lifting apparatus for use in lifting operators or materials upward for operation at the elevated spot or loading and unloading disused building materials at the building work site, and particularly to a lifting apparatus capable of lifting a platform on which heavy materials are placed to an elevated spot.
2. Prior Art
There has been employed a lifting apparatus for assembling, painting, repairing a highway, a building such as a high-rise building, and the like at an elevated spot, which apparatus is capable of lifting or lowering for loading operations or building materials and the like thereon or unloading the disused materials therefrom so that various operations at the elevated spot can be smoothly performed.
This lifting apparatus has been widely used for repairing a signal mechanism, lifting equipment, etc. at the elevated spot. In the conventional building, for repairing operations and the like at the elevated spot, a scaffold has been set up at a place close to the building wherein the operator climbs up to and down from the elevated spot along the scaffold. In the operations at the elevated spot using the scaffold, the scaffold needs to be assembled and removed, which does not make the operations quick, and creates a burden to the operator when he climbs up to and down from the elevated spot.
To solve the problem, there is proposed a lifting apparatus having a platform which is moved up and down using hydraulic pressure so as to lift or lower operators or building materials. Such a lifting apparatus dispenses with an additional work involved in assembling and removing the scaffold, which expedites the operation. Furthermore, since the operators and the building materials are moved by lifting and lowering the platform using hydraulic pressure, etc. the burden on the operator is reduced, whereby this lifting apparatus has been widely used in modern buildings.
There has been employed a pantograph type telescopic mechanism, i.e. a scissors type comprising a first pair of arms pivotally connected with each other at a central portion thereof and plural pairs of arms connected with the first pair of arms. In this apparatus, it was necessary to lengthen the length of the pairs or increase the number of arms to be connected with one another for increasing the maximum height of the apparatus. Hence, if an apparatus capable of lifting upward as high as possible is designed, it was necessary to assemble a plurality of paired pantographs vertically, which entails increasing the height of the apparatus when folded whereby it is more troublesome for an operator to get thereon or therefrom or to move materials thereon or therefrom.
There have been various proposed arrangements to solve the problems set forth above, for example the one disclosed in U.S. Pat. No. 3,820,631. In a mechanism as proposed by this patent, a lower boom and an upper boom are respectively capable of moving straight into a middle boom, the lower boom is pivotally mounted on a chassis at the end thereof, the upper boom is pivotally mounted on a platform at the end thereof, and these booms are assembled to form an X-shape. In this mechanism, inasmuch as the length of the boom per se becomes long, the height of the platform when folded can be decreased and the platform can be raised to the elevated spot.
However, in this known mechanism, inasmuch as the mechanism for extending the lower boom and upper boom from the middle boom comprises a screw and a thread for engaging with this screw, the telescopic moving speed of the lower and upper booms relative to the middle boom is slow, and hence the platform cannot be moved quickly. Furthermore, since the sliding motion of the lower boom and the upper boom is made by a bevel gear provided at the central portion of the middle boom, the entire length of the combination of the lower boom and the upper boom extending from the middle boom reaches a length only half as long as the middle boom, and hence the mechanism has such a structure that the platform cannot be raised as high as possible.
There has also been proposed a mechanism wherein another boom is inserted into a boom to extend the length thereof so that the entire length thereof is lengthened. For example, in FIG. 4 of Japanese Patent Laid-Open Publication No. 53-119556, lower and upper booms respectively having small diameters are inserted into a middle boom having a large diameter so that the lower and upper booms inserted into the middle boom are pulled out to lengthen the entire length of the booms, whereby the platform is raised high.
However, in this latter mechanism, there is no mechanism for synchronizing the amount of extension and contraction of the lower boom pulled out from the middle boom with that of the upper boom as also pulled out from the middle boom. The lower and the upper booms move individually relative to the middle boom. The amount of extension and contraction is restricted by a link mechanism comprising bars, and hence the complete synchronization of the lower and upper booms relative to the middle boom cannot be achieved. Accordingly, the lower and upper booms cannot be connected to the platform by a pin and the like and non-synchronized error of the amount of the extension and contraction between the lower and upper booms relative to the middle boom can be absorbed by rollers contacting the chassis and the platform. Hence, the platform is liable to swing because of accumulation of jolt caused by many supporting fulcrums and reception of the rolling motion by the roller. As a result, the mechanism is liable to swing due to wind and the like and is unstable, thereby causing the operator to feel anxious.
In FIG. 8 of aforesaid Japanese Patent Laid-Open Publication No. 53-19556, the middle boom which is X-shaped is turned by externally attached hydraulic cylinder wherein the lower and upper booms are pulled out from the middle boom. The amount of extension of the upper and lower booms is restricted by a link mechanism. Accordingly, hydraulic operating force of the hydraulic cylinder acts directly to the upper and lower booms, whereby the length of the upper and lower booms does not reach as long as the entire length of the middle boom when a cylinder rod of the hydraulic cylinder is pulled out at its maximum. Accordingly, it was impossible to cause the maximum length of the entire boom assembly to be extended as long as possible.
There is proposed a structure for extending the entire length of the booms from the folded state in the longitudinal direction thereof as disclosed in, for example, Japanese Patent Application No. 52-18492.
In this arrangement, an outrigger box is fixed to a part of a chassis in parallel with the chassis, wherein the outrigger box is partitioned by partition walls to form accommodating rooms in which outrigger beams are slidably inserted and in one of which an operating cylinder is accommodated. Both outrigger beams are connected to each other by a rope. In this structure, outrigger beams are pulled out from or pulled into the outrigger boxes, whereby both outrigger beams are moved in opposite directions. The length of each outrigger beam to be pulled out and extended from the outrigger box reaches a length substantially the same length as long as the outrigger box. This structure is effective to pull out the outrigger beam as long as possible from the outrigger box. This arrangement merely discloses the structure for the outriggers for fixing the chassis on the ground by floating thereof but it does not lift or lower the platform vertically even if it is applied to the lifting apparatus to be used in the elevated spot. Furthermore, in the drawings of this application, both ends of the outrigger beams are not connected to any building but merely extend and contract freely left and right in horizontal direction.
In view of the problems of the aforementioned application, there are proposed many lifting mechanisms each having an arm and a plurality of booms which are telescopically inserted into the arm so that one arm can be extended in its longitudinal direction. These are, for example, disclosed in Japanese Application No. 56-134487 and No. 56-191065 (now Laid-Open Publication No. 58-36900 and No. 58-95100).
In these proposed lifting mechanisms, three-stage booms are extended in their longitudinal directions wherein middle booms which are connected to each other at the central portion thereof by a shaft in an X-shape are turned relative to each other so that the chassis and the platform are X-shaped as viewed from the side of the lifting mechanism. In the arrangement of these lifting mechanisms, the lower and upper booms extend to reach a length substantially the same length as long as the middle boom so that the platform can be raised to the elevated spot. Since tip ends of the lower and upper booms are respectively connected to the chassis and the platform by pins, the platform has little jolt and it can be maintained strong against swinging motion.
In the lifting mechanisms using such a plurality of extendible boom assemblies which can be extended and contracted in a plurality of stages, there is provided an arrangement in which the lifting mechanism can be extended by raising the middle boom per se by a hydraulic cylinder interposed between the chassis and the center of the middle boom or pushing out the lower boom or the upper boom from the middle boom by the hydraulic cylinder inserted into the middle boom in order to extend the lower and upper booms from the middle boom or contract the lower and upper booms in the middle boom. In such a new proposed lifting apparatus, there are great advantages in that the lower and upper booms are respectively extended from or retracted into the middle boom at the both ends thereof and a pair of middle booms which are assembled at the central portion thereof are turned in the X-shape so that the platform can be lifted stably.
However, in this arrangement, the hydraulic cylinder has to be used for raising the middle booms or extending the lower and upper booms from the middle booms and the distance of the middle booms to be raised is determined by the amount of extension of the hydraulic cylinder. Accordingly, there is proposed an arrangement wherein the amount of extension of the hydraulic cylinder is doubled by a wire or chain, which increase the entire amount of extension of the upper and lower boom from the middle boom. In this arrangement, although the amount of extension can be increased by the combination of the wires or chains, the load or materials to be applied to the platform are supported by the wire or chain. As a result, the loading of the materials on the platform is concentrated on the wire or chain. Accordingly, when the materials on the platform are heavy, a large load is applied to the wire or chain when the platform is lifted. There is thus a drawback in this arrangement in that the load to be lifted by the platform cannot be increased even if the platform can be lifted high because of the load limitations imposed by the wire.
An arrangement of the type briefly described above is shown in U.S. Pat. No. 5,099,950.
In the structure of the mechanism for vertically moving the platform by the telescopic boom assembly which is assembled in the X-shape, there are advantages in that swing or jolt of the platform is less likely to occur, and the number of the booms to be used is small so that the platform can be raised stably, but a disadvantage in that the height of the platform to be raised is determined by the amount of extension of the hydraulic cylinder. In the double speed mechanism using the wire or chain, there are contrary disadvantages in that the amount of extension of the platform can be increased but the load or materials to be raised by the platform cannot be increased. Accordingly, there is desired a lifting mechanism having different performances so that the platform can be raised to the elevated spot using a hydraulic cylinder while carrying heavy materials thereon.